Is this crazy? I've always wanted a little more speed using the 9.9 Merc outboard on my C-25, so what's wrong with putting on a 25hp outboard? Is it the weight? Is it the thrust? It seems that a little more power could maybe push my C-25 up to 10 kts. when motorsailing. Thoughts?
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Hull speed
Your not going to get much more than your calculated maximum hull speed and that's calculated as 6.31 knots. Admittedly, that's a theoretic, calculated speed and actual speed over ground will vary due to conditions but adding that much more weight to the transom sure isn't going to improve performance. The weight aft will likely counter whatever additional thrust you might get. So, when you do the math about the relative cost of a 25hp vs. a 9.9hp, it doesn't add up. Besides, gas is $3.50/gallon.
Your not going to get much more than your calculated maximum hull speed and that's calculated as 6.31 knots. Admittedly, that's a theoretic, calculated speed and actual speed over ground will vary due to conditions but adding that much more weight to the transom sure isn't going to improve performance. The weight aft will likely counter whatever additional thrust you might get. So, when you do the math about the relative cost of a 25hp vs. a 9.9hp, it doesn't add up. Besides, gas is $3.50/gallon.
Thanks
Thanks, That makes sense. I have a follow-up question: what about putting a larger prop on it to give more initial thrust?
Thanks, That makes sense. I have a follow-up question: what about putting a larger prop on it to give more initial thrust?
C25 Info
For more info on the C25, check out the International Association, especially the Sailor's Forums. You won't find a better resource anywhere. Click on the Related Link...
For more info on the C25, check out the International Association, especially the Sailor's Forums. You won't find a better resource anywhere. Click on the Related Link...
Keep in mind that a 25 will probably generate
approximately 2x the thrust that a 9.9 will produce and that puts a LOT more stress on a transom than it was designed for. Also, as John pointed out, the weight aft will be much greater. A 25 hp 4 stroke weighs 180 lbs and a 2 stroke weighs in at 105. Have you considered what kind of bracket would be required to support a 25hp motor? A shallower-pitched prop could make response better at slower speeds and would probably be the better choice for getting into and out of slips.
approximately 2x the thrust that a 9.9 will produce and that puts a LOT more stress on a transom than it was designed for. Also, as John pointed out, the weight aft will be much greater. A 25 hp 4 stroke weighs 180 lbs and a 2 stroke weighs in at 105. Have you considered what kind of bracket would be required to support a 25hp motor? A shallower-pitched prop could make response better at slower speeds and would probably be the better choice for getting into and out of slips.
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